Lithium batteries

ABSTRACT

Provided is a lithium battery in which the cathode comprises an electroactive sulfur-containing material and the electrolyte comprises a lithium salt, a non-aqueous solvent, and one or more capacity-enhancing reactive components. Suitable reactive components include electron                    
     transfer mediators of the formula: 
     wherein: R 4  is the same or different at each occurrence and is selected from the group consisting of H, alkyl, alkenyl, aryl, or substituted derivatives thereof; E is the same or different at each occurrence and is selected from the group consisting of O, NR 5 , and S; where R 5  is alkyl, aryl, or substituted derivatives thereof; a is an integer from 0 to 1; and r is an integer from 2 to 5. Also are provided methods for making the lithium battery.

RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/165,368, filed Nov. 12, 1999, the disclosure of which isincorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates generally to the field of electrochemicalcells. More particularly, this invention pertains to lithium batteriesin which the cathode comprises an electroactive sulfur-containingmaterial and the electrolyte comprises reactive components that enhancethe capacity of the lithium battery.

BACKGROUND

Throughout this application, various publications, patents, andpublished patent applications are referred to by an identifyingcitation. The disclosures of the publications, patents, and publishedpatent specifications referenced in this application are herebyincorporated by reference into the present disclosure to more fullydescribe the state of the art to which this invention pertains.

As the evolution of batteries continues, and particularly as lithiumbatteries become more widely accepted for a variety of uses, the needfor safe, long lasting high energy batteries becomes more important.There has been considerable interest in recent years in developing highenergy density cathode-active materials for use in high energy primaryand secondary batteries with lithium containing anodes. Various types ofcathode materials for the manufacture of lithium batteries are known inthe art.

One class of lithium batteries known in the art are rechargeable lithiumbatteries where the battery is able to undergo multiple discharge andrecharge cycles. During discharge of a lithium cell, lithium ions areformed and extracted from the anode and inserted into the cathode. Onrecharge, the reverse process occurs. The electrodes used in thesebatteries can have a dramatic effect on the performance of the batteryand, in particular, on cycle life.

Another class of lithium batteries known in the art are primary lithiumbatteries. A primary battery differs from a rechargeable battery in thatit is only designed to be discharged once. In fact, because of thedesign, attempts to recharge a primary battery may create safetyproblems and may be only partially effective for a very limited numberof cycles. Examples of lithium primary cells are described by Nishio etal. in Handbook of Battery Materials, Chapter 2, “Practical Batteries”,pp. 31-40, Elsevier, Amsterdam, (1999) and by Linden in Handbook ofBatteries, Chapter 14, pp. 5-6, McGraw-Hill, N.Y. (1995). Primary,non-rechargeable cells, with their single discharge, have a shortlifetime and their disposal burden is high, which makes the choice ofthe cathode material and its impact on the environment of greatimportance. Sulfur is an attractive cathode-active material for primarycells, both from an environmental perspective and from its very hightheoretical specific capacity of 1675 mAh/g in the lithium-sulfurcouple.

U.S. Pat. No. 4,410,609 to Peled et al. describes a primary cellcomprising an anode consisting of lithium or a dischargeable alloy oflithium, an electrolyte comprising a solvent to dissolve both anelectrolyte salt and polysulfides at a low concentration, and an inertporous cathode current collector, which may be loaded with sulfur. Yaminet al., in Electrochemical Society Proceedings, 1984, Volume 84-1,301-310, describe low rate lithium/sulfur batteries in which the primarycells have a porous carbon cathode current collector impregnated withsulfur and in which the cell's electrolyte is a lithium polysulfidesaturated solution of 1M LiClO₄ in tetrahydrofuran-toluene mixtures. Theroom temperature energy density for these cells is reported to be 730Wh/Kg.

In a study of dioxolane-based solvents for lithium-sulfur batteries,Peled et al., in J. Electrochem. Soc., 1989, 136, 1621-1625, report thatdioxolane-rich solvents are compatible with lithium but that sulfurutilization is only 50% due to the final reduction (discharge) product,Li₂S₂.

There is a need to enhance the performance of primary and rechargeablelithium electrochemical cells. In studies on lithium/thionyl chloridecells, performance enhancement has been achieved by the addition ofhalide additives. For example, Linden, in Handbook of Batteries, Chapter14, pp. 44-47, McGraw-Hill, New York (1995), summarizes data showing anincrease in cell voltage and energy density by the addition of BrCl tolithium/thionyl chloride cells. In U.S. Pat. Nos. 4,784,925 and4,784,927 to Klinedinst et al., small quantities of iodine or iodinemonochloride are reported to act as catalysts to increase output voltageand output capacity of lithium/thionyl chloride cells.

Sodium-sulfur cells, which typically operate at high temperatures, suchas 300° C. to 350° C., also typically operate at a capacity less thantheoretical to avoid precipitation of insoluble Na₂S and Na₂S₂. U.S.Pat. No. 4,018,969 to Fisher et al., and U.S. Pat. Nos. 4,184,013,4,216,276, and 4,238,553 to Weddigen et al. describe additives whichincrease the solubility of Na₂S and Na₂S₂ in the liquid sulfur cathodeand thereby increase the capacity of high temperature sodium-sulfurcells.

Despite the various approaches proposed for the fabrication of lithiumcells, there remains a need for higher energy density and safer and moreenvironmentally acceptable primary and rechargeable lithium cells.

It is, therefore, an object of the present invention to provide lithiumcells which have higher energy density.

It is another object of the present invention to provide cells which aresafe and which comprise environmentally acceptable materials.

SUMMARY OF THE INVENTION

The present invention pertains to a lithium electrochemical cellcomprising: (a) a solid lithium anode; (b) a solid cathode comprising anelectroactive sulfur-containing material; and (c) a non-aqueouselectrolyte interposed between the solid anode and the solid cathode,which electrolyte comprises: (i) one or more lithium salts; (ii) one ormore non-aqueous solvents; and (iii) one or more capacity-enhancingreactive components.

In one embodiment, the one or more capacity-enhancing reactivecomponents comprise an anion receptor. In one embodiment, the one ormore capacity-enhancing reactive components comprise an electrontransfer mediator.

In one embodiment, the anion receptor comprises a polyalkyleneaminecompound of the formula (—N(R)—CH₂—CH₂—)_(q), where q is an integerequal to or greater than 2, and R is a substituent selected from thegroup consisting of CF₃SO₂, CF₃CO, CN, SO₂CN, and (—CH₂—CH₂—N(R¹)—)_(p),where R¹ is selected from the group consisting of H, CF₃SO₂, CF₃CO, CN,and SO₂CN, and p is an integer from 1 to 4.

In one embodiment, the anion receptor is a boron moiety, BX₃, where X,is the same or different at each occurrence and is an electronwithdrawing moiety selected from the group consisting of F,perfluoroalkyl, CF₂═CF—, pentafluorophenyl, 3,4,5-trifluorophenyl,CF₃SO₂, N(CF₃SO₂)₂, C(CF₃SO₂)₃, and

where R² is the same or different at each occurrence and is selectedfrom the group consisting of H, F, CF₃, COCF₃, SO₂CF₃, and SO₂F.

In one embodiment, the anion receptor is present in the amount of 0.2%to 25% by weight of the electrolyte. In one embodiment, the anionreceptor is present in the amount of 0.5% to 10% by weight of theelectrolyte.

In one embodiment, the capacity-enhancing reactive component comprisescomponents of formula:

wherein:

R⁴ is the same or different at each occurrence and is selected from thegroup consisting of H, alkyl, alkenyl, aryl, or substituted derivativesthereof;

E is the same or different at each occurrence and is selected from thegroup consisting of O, NR⁵, and S, where R⁵ is alkyl, aryl, orsubstituted derivatives thereof;

a is an integer from 0 to 1; and

r is an integer from 2 to 5.

In one embodiment, the electron transfer mediator is of the formula:

wherein:

Z is the same or different at each occurrence and is selected from thegroup consisting of O, S, Se, and NR⁵, where R⁵ is alkyl, aryl, orsubstituted derivatives thereof;

R is the same or different at each occurrence, is selected from thegroup consisting of alkyl, aryl, F, Cl, CF₃, CF₃SO₂, and N(R⁵)₂, whereR⁵ is alkyl, aryl, or substituted derivatives thereof;

Y is —C═C— or

and

t is an integer from 0 to 4.

In another embodiment, the electron transfer mediator is of the formula:

wherein:

Z is the same or different at each occurrence and is selected from thegroup consisting of O, S, Se, and NR⁵, where R⁵ is alkyl, aryl, orsubstituted derivatives thereof;

R is the same or different at each occurrence and is selected from thegroup consisting of alkyl, aryl, F, Cl, CF₃, CF₃SO₂, and N(R⁶)₂, whereR⁶ is alkyl, aryl, or substituted derivatives thereof;

Y is —C═C— or

and

u is an integer from 1 to 6.

In one embodiment, the electron transfer mediator is present in theamount of 0.2% to 25% by weight of the electrolyte. In one embodiment,the electron transfer mediator is present in the amount of 0.5% to 10%by weight of the electrolyte.

In one embodiment, the electron transfer mediator has anoxidation-reduction potential less than 2.2 V. In a preferredembodiment, the electron transfer mediator has an oxidation-reductionpotential in the range of 1.5 V to about 2.0 V.

In one embodiment, the one or more non-aqueous solvents are selectedfrom the group consisting of ethers, cyclic ethers, polyethers,sulfones, and sulfolanes.

In one embodiment, the one or more lithium salts are selected from thegroup consisting of LiBr, LiI, LiSCN, LiBF₄, LiPF₆, LiAsF₆, LiSO₃CF₃,LiN(SO₂CF₃)₂, LiC(SO₂CF₃)₃, (LiS_(x))_(z)R, and Li₂S_(x), where x is aninteger from 1 to 20, z is an integer from 1 to 3, and R is an organicgroup.

In one embodiment, the electroactive sulfur-containing materialcomprises elemental sulfur. In one embodiment, the electroactivesulfur-containing material, in its oxidized state, comprises one or morepolysulfide moieties, —S_(m)—, where m is an integer equal to or greaterthan 3. In one embodiment, the electroactive sulfur-containing material,in its oxidized state, comprises one or more polysulfide moieties,—S_(m) ⁻, where m is an integer equal to or greater than 3. In oneembodiment, the electroactive sulfur-containing material, in itsoxidized state, comprises one or more polysulfide moieties, —S_(m) ²⁻,where m is an integer equal to or greater than 3.

In one embodiment, the electroactive sulfur-containing material, in itsoxidized state, is of the general formula:

C(S_(x))_(n)

wherein x ranges from greater than 2.5 to about 50, and n is an integerequal to or greater than to 2.

In one embodiment, the electroactive sulfur-containing material, in itsoxidized state, comprises one or more of the polysulfur moieties:

wherein m, the same or different at each occurrence, is an integer andis greater than 2, and y, the same or different at each occurrence, isan integer and is equal to or greater than 1.

In one embodiment, the electroactive sulfur-containing material, in itsoxidized state, comprises one or more of the moieties:

wherein m is the same or different at each occurrence and is greaterthan 2.

In one embodiment, the electroactive sulfur-containing material is apolymer comprising polymeric segments of the formula;

wherein:

Q denotes a carbocyclic repeat unit comprising a carbocycle having from3 to 12 ring carbon atoms;

S denotes a sulfur atom;

m is the number of sulfur atoms in a given polysulfide linkage, is aninteger from 3 to 10, and is the same or different at each occurrence;

n denotes the number of crosslinking polysulfide linkages, is an integerfrom 1 to 20, and is the same or different at each occurrence; and

v is an integer greater than 1.

In one embodiment, the electroactive sulfur-containing materialcomprises greater than 50% by weight of sulfur. In a preferredembodiment, the electroactive sulfur-containing material comprisesgreater than 75% by weight of sulfur. In a more preferred embodiment,the electroactive sulfur-containing material comprises greater than 90%by weight of sulfur.

In one embodiment, the lithium anode is selected from the groupconsisting of lithium metal, lithium-aluminum alloys, lithium-tinalloys, lithium-intercalated carbons, and lithium-intercalatedgraphites.

In one embodiment, the cell has an energy density of greater than 1000Wh/Kg. In one embodiment, the cell has an energy density of greater than1200 Wh/Kg. In one embodiment, the cell has an energy density greaterthan 1500 Wh/Kg.

In one embodiment of the present invention, the capacity-enhancingreactive components increase the discharge capacity of the firstcharge-discharge cycle of the cell by greater than 10%. In oneembodiment of the present invention, the capacity-enhancing reactivecomponents increase the total discharge capacities of 30charge-discharge cycles of the cell by greater than 10%. In oneembodiment, the capacity-enhancing reactive components increase thetotal discharge capacities of 30 charge-discharge cycles of the cell bygreater than 30%.

In one embodiment, the cell is a secondary electrochemical cell. In oneembodiment, the cell is a primary electrochemical cell.

Another aspect of the present invention pertains to a method of making alithium electrochemical cell comprising the steps of: (a) providing asolid lithium anode; (b) providing a solid cathode comprising anelectroactive sulfur-containing material; and (c) interposing anon-aqueous electrolyte between the anode and the cathode, wherein theelectrolyte comprises: (i) one or more lithium salts; (ii) one or morenon-aqueous solvents; and (iii) one or more capacity-enhancing reactivecomponents, as described herein.

As will be appreciated by one of skill in the art, features of oneaspect or embodiment of the invention are also applicable to otheraspects or embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present invention pertains to electrochemical cellscomprising: (a) a solid lithium anode; (b) a solid cathode comprising anelectroactive sulfur-containing material; and (c) a non-aqueouselectrolyte interposed between the anode and the cathode, wherein theelectrolyte comprises: (i) one or more lithium salts; (ii) one or morenon-aqueous solvents; and (iii) one or more capacity-enhancing reactivecomponents. In one embodiment, the one or more capacity-enhancingreactive components comprise an anion receptor. In one embodiment, theone or more capacity-enhancing reactive components comprise an electrontransfer mediator. The capacity-enhancing reactive components may benon-electroactive or electroactive. The term “non-electroactive,” asused herein, pertains to a cell component material which does not takepart in the electrochemical reaction of discharge in the absence of anelectroactive sulfur-containing cathode material.

Capacity-enhancing Electrolyte Reactive Components

In the present invention, capacity-enhancing reactive components areadded to the non-aqueous electrolyte of a lithium/electroactivesulfur-containing material electrochemical cell to increase theelectrochemical capacity of the cell. For an electrochemical cell basedon lithium and elemental sulfur, the theoretical energy density is 2,600Wh/Kg. In one example, the capacity limit for a lithium/elemental sulfurcell is about 730 Wh/Kg (calculated on the basis of all cell components,excluding the case) as reported by Yamin et al. in ElectrochemicalSociety Proceedings, 1984, Volume 84-1, 301-310. Typically, the capacityis limited by the insolubility and electronic non-conductivity of Li₂S₂,a reduction product of the cell, which prevents the complete reductionof S₈ to Li₂S. It can be seen that approximately 50% of the theoreticalcapacity is lost if the electrochemical reaction stops at Li₂S₂. Inother words, to extract maximum capacity from the cell, Li₂S₂ must bereduced to Li₂S.

One route by which the capacity-enhancing reactive components of thepresent invention enhance the capture of the theoretical capacity of thelithium/sulfur-type cells of the present invention is by increasing thesolubility of Li₂S₂. The solubility of Li₂S₂ may be increased by the useof anion receptors to react or complex with the Li₂S₂ produced duringdischarge. Suitable anion receptors include, but are not limited to, theammonium, amide and Lewis acid materials described by Dietrich in Pureand Applied Chemistry, 1993, 65, 1457-1464, such as polyammoniummacrocycles, polyammonium macrobicycles, polyammonium macrotricycles,guanidinium materials, amide functional molecules, and Lewis acidmaterials. Lee et al. in U.S. Pat. Nos. 5,705,689 and 5,789,585 describepolyalkyleneamine derivatives as anion receptors which increase theionic conductivity of solutions of lithium salts in non-aqueoussolvents, for example, LiCl and LiBr in tetrahydrofuran. Lee et al. inJ. Electrochem. Soc., 1998, 145, 2813-2818, describe borate ester anionreceptors which increase the ionic conductivity of solutions of lithiumsalts, for example, lithium trifluoroacetate, LiF, LiCl, and Lil, indimethoxyethane.

Suitable capacity-enhancing reactive components of the present inventionfor use as anion receptors include, but are not limited to, linear,branched, and cyclic polyalkyleneamines, of the formula(—N(R)—CH₂—CH₂—)_(q), where R is a moiety selected from the group ofelectron withdrawing groups, such as, CF₃SO₂, CF₃CO, CN, SO₂CN, and q isan integer from 1 to 20; or R is (—CH₂—CH₂—N(R¹)—)_(p), where R¹ is H,CF₃SO₂, CF₃CO, CN, and SO₂CN, and p is an integer from 1 to 4, asdescribed, for example, by Lee et al. in U.S. Pat. Nos. 5,705,689 and5,789,585. Further suitable capacity-enhancing reactive components foruse as anion receptors include compositions with NCF₃, NSO₂F, NSO₂CF₃,and NCF₂N functionality, as described, for example, in U.S. Pat. No.4,216,276 to Weddigen et al.

Suitable Lewis acid anion receptors include, but are not limited to,boron, tin, and silicon moieties. For example, boron moieties, BX₃,where X, is the same or different at each occurrence and is an electronwithdrawing moiety selected from the group consisting of F,perfluoroalkyl, CF₂═CF—, pentafluorophenyl, 3,4,5-trifluorophenyl,CF₃SO₂, N(CF₃SO₂)₂, C(CF₃SO₂)₃, and

where R² is the same or different at each occurrence, and is selectedfrom the group consisting of H, F, CF₃, COCF₃, SO₂CF₃, and SO₂F.

The amount of the anion receptor may vary over a wide range from about0.2% by weight of the total electrolyte components to about 25% byweight. Preferably the amount is from about 0.5% by weight to about 10%by weight. More preferably the amount is from about 1% by weight toabout 5% by weight.

Although any of the suitable anion receptors may be used, in eachsituation the most effective choice will depend on the particularelectrolyte solvent system and electrolyte salt.

An alternative route to enhance the capture of the theoretical capacityof the lithium/sulfur-type cells of the present invention is by theaddition of an electron transfer mediator to the electrolyte for thereduction of Li₂S₂ to Li₂S. Effective mediators are those whoseoxidation-reduction potential is below 2.2 V. Most preferably, themediators have an oxidation-reduction potential in the range of 1.5 V to2.0 V.

While not wishing to be bound by any theory, the electron transfermediators may function by accepting a pair of electrons in anelectrochemical reduction process at a voltage in the range of 1.5 V to2.0 V, and in turn transferring the electrons to Li₂S₂ with theformation of lithium sulfide, Li₂S, liberation of sulfide ion, S²⁻, andregeneration of the mediator, M. The process may described as:

M+2e ⁻→M²⁻

M²⁻+Li₂S₂→Li₂S+S²⁻+M

Alternatively, the electron transfer mediators may function by acceptinga single electron in an electrochemical reduction process at a voltagein the range of 1.5 V to 2.0 V and in turn transferring an electron toLi₂S₂. In a subsequent step, a second electron transfer may take placecompleting the reduction of Li₂S₂ to Li₂S+S²⁻. The mediator remainsunchanged in this cycle. This process may be described as:

M+e ^(−→M) ^(•−)

M^(•−)+Li₂S₂→Li₂S₂ ^(•−)+M

Li₂S₂ ^(•−)+M^(•−→Li) ₂S₂+S²⁻+M

where M represents an electron transfer mediator.

Suitable electron transfer mediators include, but are not limited to,those of formula I:

wherein:

R⁴ is the same or different at each occurrence and is selected from thegroup consisting of H, alkyl, alkenyl, aryl, or substituted derivativesthereof;

E is the same or different at each occurrence and is selected from thegroup consisting of O, NR⁵, and S, where R⁵ is alkyl, aryl, orsubstituted derivatives thereof;

a is an integer from 0 to 1; and

r is an integer from 2 to 5.

Suitable electron transfer mediators of formula I include, but are notlimited to, bis(methoxymethyl)disulfide, bis(methoxymethyl)trisulfide,bis(methoxymethyl)polysulfide, bis(methoxyethyl)disulfide,bis(methoxyethyl)trisulfide, bis(methoxyethyl)polysulfide,bis(3-allyloxy-2-hydroxypropyl)disulfide,bis(3-allyloxy-2-hydroxypropyl)trisulfide,bis(3-allyloxy-2-hydroxypropyl)tetrasulfide,bis(vinyloxyethoxy-2-hydroxypropyl)disulfide,bis(vinyloxyethoxy-2-hydroxypropyl)trisulfide,bis(vinyloxyethoxy-2-hydroxypropyl)polysulfide,bis(2-hydroxy-2-phenylethyl)disulfide,bis(2-hydroxy-2-phenylethyl)trisulfide,bis(2-hydroxy-2-phenylethyl)polysulfide,bis(N,N-dimethylaminoethyl)disulfide,bis(N,N-diethylaminoethyl)disulfide,bis(N,N-dimethylaminoethyl)trisulfide,bis(N,N-diethylaminoethyl)trisulfide, andbis(N,N-dimethylaminoethyl)polysulfide.

Suitable electron transfer mediators also include, but are not limitedto, those of formula II:

wherein:

Z is the same or different at each occurrence and is selected from thegroup consisting of O, S, Se, and NR⁵, where R⁵ is alkyl, aryl, orsubstituted derivatives thereof;

R is same or different at each occurrence and is selected from the groupconsisting of alkyl, aryl, F, Cl, CF₃, CF₃SO₂, and N(R⁵)₂, where R⁵ isalkyl, aryl, or substituted derivatives thereof and is the same ordifferent at each occurrence;

Y is—C═C— or

and

t is an integer from 0 to 4.

Suitable electron transfer mediators also include, but are not limitedto, those of formula III:

wherein:

Z is the same or different at each occurrence and is selected from thegroup consisting of O, S, Se, and NR⁵, where R⁵ is alkyl, aryl, orsubstituted derivatives thereof;

R is the same or different at each occurrence and is selected from thegroup consisting of alkyl, aryl, F, Cl, CF₃, CF₃SO₂, and N(R⁵)₂, whereR⁵ is alkyl, aryl, or substituted derivatives thereof and is the same ordifferent at each occurrence;

Y is —C═C— or

and

u is an integer from 1 to 6.

Other examples of suitable electron transfer mediators includetransition metal complexes, including but not limited to, complexes ofphthalocyanines and porphyrins with transition metals, including but notlimited to, iron, cobalt, manganese, vanadium, copper, chromium, andnickel, where the complexes are soluble in the electrolyte.

Other examples of suitable electron transfer mediators includebis-pyridinium salts, also known as viologens, and polynuclear aromatichydrocarbons which can form radical anions upon reduction, where thebis-pyridinium salts and the polynuclear aromatic hydrocarbons aresoluble in the electrolyte.

Although any of the suitable electron transfer mediators may be used, ineach situation the most effective choice will depend on the solubilityand compatibility of the electron transfer mediator with the particularelectrolyte solvent system, the electrolyte salt, and the reductionproducts of the sulfur-containing cathode material.

The amount of the electron transfer mediator may vary over a wide rangefrom 0.2% by weight of the total electrolyte components to about 25% byweight. Preferably the amount is from about 0.5% by weight to about 10%by weight. More preferably the amount is from about 1% by weight toabout 5% by weight

In another embodiment of the present invention, an electron transfermediator may be formed in the electrochemical cell from the reaction ofreduction products of the sulfur-containing cathode materials with aprecursor moiety. Suitable precursor moieties will possess highreactivity toward cathode reduction products such as, for example,polysulfide anions but be unreactive or possess low reactivity towardelectrolyte components. Examples of suitable precursor moieties include,but are not limited to, haloalkyl ethers, haloalkyl amines, alkylepoxides, aryl epoxides, and glycidyl ethers. Haloalkyl ethers includechloromethyl methyl ether, chloromethyl ethyl ether, chloromethyl benzylether, chloroethyl methyl ether, bis(chloromethyl) ether, and thecorresponding bromo-derivatives. Haloalkyl amines includeN,N-dimethyl-2-chloroethylamine, N,N-diethyl-2-chloroethylamine, andN,N-dimethyl-2-bromoethylamine. Epoxides include propylene oxide,butylene oxide, and styrene oxide. Glycidyl ethers include methylglycidyl ether, ethyl glycidyl ether, and ethylene glycol methylglycidyl ether.

The capacity-enhancing reactive components of the present invention areadded to the electrolyte, which comprises one or more non-aqueoussolvents and one or more ionic electrolyte salts.

In one embodiment of the present invention, the energy density of thecell is greater than 1000 Wh/Kg. In another embodiment, the energydensity of the cell is greater than 1200 Wh/Kg. In a preferredembodiment, the energy density of the cell is greater than 1500 Wh/Kg.The term “energy density,” as used herein, relates to cell energy basedon the sum of the weights of the anode active components, the cathodeactive components, and the capacity-enhancing reactive components.

In one embodiment of the present invention, the capacity-enhancingreactive components increase the discharge capacity of the firstcharge-discharge cycle of the cell by greater than 10%. In oneembodiment of the present invention, the capacity-enhancing reactivecomponents increase the total discharge capacities of 30charge-discharge cycles of the cell by greater than 10%. In a preferredembodiment of the present invention, the capacity-enhancing reactivecomponents increase the total discharge capacities of 30charge-discharge.cycles of the cell by greater than 30%.

The electrolytes of the electrochemical cells of the present inventioncomprising one or more capacity-enhancing reactive components mayadditionally comprise voltage-enhancing reactive components, for exampleas described in co-pending U.S. patent application Ser. No. 09/709,778,now abandoned, and published as International Publication No. WO01/35475, entitled “Lithium Primary Batteries” to Mikhaylik et al. ofthe common assignee, both filed on even date herewith.

Cathodes

The term “electroactive sulfur-containing material,” as used herein,relates to cathode active materials which comprise the element sulfur inany form, wherein the electrochemical activity involves the breaking orforming of sulfur-sulfur covalent bonds.

Examples of suitable electroactive sulfur-containing materials, include,but are not limited to, elemental sulfur and organic materialscomprising both sulfur atoms and carbon atoms, which may or may not bepolymeric. Suitable organic materials include those further comprisingheteroatoms, conductive polymer segments, composites, and conductivepolymers.

In one embodiment, the electroactive sulfur-containing materialcomprises elemental sulfur. In one embodiment, the electroactivesulfur-containing material comprises a mixture of elemental sulfur and asulfur-containing polymer.

In one embodiment, the sulfur-containing material, in its oxidizedstate, comprises a polysulfide moiety, S_(m), selected from the groupconsisting of covalent —S_(m)— moieties, ionic —S_(m)− moieties, andionic S_(m) ²⁻ moieties, wherein m is an integer equal to or greaterthan 3, such as for example, elemental sulfur and sulfur-containingpolymers. In one embodiment, m of the polysulfide moiety, S_(m), is aninteger equal to or greater than 6. In one embodiment, m of thepolysulfide moiety, S_(m), is an integer equal to or greater than 8. Inone embodiment, the sulfur-containing material is a sulfur-containingpolymer. In one embodiment, the sulfur-containing polymer has a polymerbackbone chain and the polysulfide moiety, S_(m), is covalently bondedby one or both of its terminal sulfur atoms as a side group to thepolymer backbone chain. In one embodiment, the sulfur-containing polymerhas a polymer backbone chain and the polysulfide moiety, S_(m), isincorporated into the polymer backbone chain by covalent bonding of theterminal sulfur atoms of the polysulfide moiety.

The specific capacity (mAh/g or Ah/Kg) or energy density (Wh/Kg) inelectroactive sulfur-containing materials is directly related to thenumber of electrons participating in the reduction/oxidation(discharge/charge) process. For a disulfide group, (R′-S-S-R″, where R′and R″ are independently an organic group), two electrons participate inthe discharge/charge process. For higher polysulfides, two electronsparticipate in each sulfur-sulfur bond reduction. It can be readilyappreciated that increased energy densities are obtained in higherpolysulfides compared with disulfides.

In one embodiment, the electroactive sulfur-containing materialcomprises greater than 50% by weight of sulfur. In a preferredembodiment, the electroactive sulfur-containing material comprisesgreater than 75% by weight of sulfur. In a more preferred embodiment,the electroactive sulfur-containing material comprises greater than 90%by weight of sulfur.

The nature of the electroactive sulfur-containing materials useful inthe practice of this invention may vary widely. Further examples ofsuitable electroactive sulfur-containing materials include, but are notlimited to:

(a) an electroactive polycarbon-sulfide material, which in its oxidizedstate, is of the general formula:

C(S_(x))_(n)

wherein x ranges from greater than 2.5 to about 50, and n is an integerequal to or greater than 2, as described in U.S. Pat. Nos. 5,601,947 and5,690,702 to Skotheim et al.; and which, in its oxidized state, maycomprise one or more of the polysulfur moieties:

wherein m, the same or different at each occurrence, is an integer andis greater than 2, and y, the same or different at each occurrence, isan integer and is equal to or greater than 1;

(b) an electroactive polyacetylene co-polysulfur material, which, in itsoxidized state, is of the general formula:

 wherein x ranges from greater than 1 to about 100, and n is an integerequal to or greater than 2, as described in U.S. Pat. Nos. 5,529,860 and6,117,590 to Skotheim et al., and which, in its oxidized state, maycomprise one or more of the moieties:

 wherein m, the same or different at each occurrence, is greater than 2;and

(c) an electroactive, highly crosslinked organic polymer, which polymercomprises polymeric segments of the formula;

wherein:

Q denotes a carbocyclic repeat unit comprising a carbocycle having from3 to 12 ring carbon atoms;

S denotes a sulfur atom;

m is the number of sulfur atoms in a given polysulfide linkage, is aninteger from 3 to 10, and is the same or different at each occurrence;

n denotes the number of crosslinking polysulfide linkages, is an integerfrom 1 to 20, and is the same or different at each occurrence; and

v is an integer greater than 1; as described in U.S. patent applicationSer. No. 08/995,122, now U.S. Pat. No. 6,201,100, to Gorkovenko et al.of the common assignee and PCT Publication No. WO 99/33130.

Other suitable electroactive sulfur-containing materials comprisingpolysulfide linkages include, but are not limited to, those described inU.S. Pat. No. 4,664,991 to Perichaud et al. and in U.S. Pat. Nos.5,723,230, 5,783,330, 5,792,575 and 5,882,819 to Naoi et al.

Other examples of suitable electroactive sulfur-containing polymersinclude organo-sulfur materials comprising disulfide linkages, althoughtheir low specific capacity compared to the corresponding materialscomprising polysulfide linkages makes it highly difficult to achieve thehigh capacities desired for practical electrochemical cells. However,they may be utilized in a blend with elemental sulfur and/or withsulfur-containing polymers comprising a polysulfide moiety in thecathodes of this invention, and may contribute by their electrochemicalproperties, by their interaction with lithium polysulfides and lithiumsulfides generated during the cycling of the cells, and, optionally, bytheir melting properties during cell fabrication, to achieve the desiredhigh capacities in the electrochemical cells or batteries of the presentinvention. Examples of electroactive sulfur-containing materialscomprising disulfide groups include those described in U.S. Pat. No.4,739,018 to Armand et al.; U.S. Pat. Nos. 4,833,048 and 4,917,974, bothto De Jonghe et al.; U.S. Pat. Nos. 5,162,175 and 5,516,598, both toVisco et al.; and U.S. Pat. No. 5,324,599 to Oyama et al.

The cathodes of the lithium cells of the present invention may furthercomprise one or more conductive fillers to provide enhanced electronicconductivity. Examples of conductive fillers include, but are notlimited to, those selected from the group consisting of conductivecarbons, graphites, activated carbon fibers, non-activated carbonnanofibers, metal flakes, metal powders, metal fibers, carbon fabrics,metal mesh, and electrically conductive polymers. The amount ofconductive filler, if present, is preferably in the range of 2 to 30% byweight. The cathodes of the present invention may also further compriseother additives such as, for example, metal oxides, aluminas, silicas,and transition metal chalcogenides.

The cathodes of the lithium cells of the present invention may alsocomprise a binder. The choice of binder material may vary widely so longas it is inert with respect to the other materials in the cathode.Useful binders are those materials, usually polymeric, that allow forease of processing of battery electrode composites and are generallyknown to those skilled in the art of electrode fabrication. Examples ofuseful binders include, but are not limited to, those selected from thegroup consisting of polytetrafluoroethylenes (Teflon®), polyvinylidenefluorides (PVF₂ or PVDF), ethylene-propylene-diene (EPDM) rubbers,polyethylene oxides (PEO), UV curable acrylates, UV curablemethacrylates, and heat curable divinyl ethers, and the like. The amountof binder, if present, is preferably in the range of 2 to 30% by weight.

The cathodes of the lithium cells of the present invention may furthercomprise a current collector as known in the art. Current collectors areuseful in efficiently collecting the electrical current generatedthroughout the cathode and in providing an efficient surface forattachment of the electrical contacts leading to the external circuit aswell as functioning as a support for the cathode. Examples of usefulcurrent collectors include, but are not limited to, those selected fromthe group consisting of metallized plastic films, metal foils, metalgrids, expanded metal grids, metal mesh, metal wool, woven carbonfabric, woven carbon mesh, non-woven carbon mesh, and carbon felt.

Cathodes of the lithium cells of the present invention may be preparedby a variety of methods. For example, one suitable method comprises thesteps of: (a) dispersing or suspending in a liquid medium theelectroactive sulfur-containing material, as described herein; (b)optionally adding to the mixture of step (a) a conductive filler,binder, or other cathode additives; (c) mixing the compositionresultingfrom step (b) to disperse the electroactive sulfur-containingmaterial; (d) casting the composition resulting from step (c) onto asuitable substrate; and (e) removing some or all of the liquid from thecomposition resulting from step (d) to provide the cathode.

Examples of suitable liquid media for the preparation of cathodes of thepresent invention include aqueous liquids, non-aqueous liquids, andmixtures thereof. Especially preferred liquids are non-aqueous liquidssuch as, for example, methanol, ethanol, isopropanol, propanol, butanol,tetrahydrofuran, dimethoxyethane, acetone, toluene, xylene,acetonitrile, and cyclohexane.

Mixing of the various components can be accomplished using any of avariety of methods known in the art so long as the desired dissolutionor dispersion of the components is obtained. Suitable methods of mixinginclude, but are not limited to, mechanical agitation, grinding,ultrasonication, ball milling, sand milling, and impingement milling.

The formulated dispersions can be applied to substrates by any of avariety of coating methods known in the art and then dried usingtechniques, known in the art, to form the solid cathodes of the lithiumcells of this invention. Suitable hand coating techniques include, butare not limited to, the use of a wire-wound coating rod or gap coatingbar. Suitable machine coating methods include, but are not limited to,the use of roller coating, gravure coating, slot extrusion coating,curtain coating, and bead coating. Removal of some or all of the liquidfrom the mixture can be accomplished by any of a variety of means knownin the art. Examples of suitable methods for the removal of liquids fromthe mixture include, but are not limited to, hot air convection, heat,infrared radiation, flowing gases, vacuum, reduced pressure, and bysimply air drying.

The method of preparing the cathodes of the present invention mayfurther comprise heating the electroactive sulfur-containing material toa temperature above its melting point and then resolidifying the meltedelectroactive sulfur-containing material to form a cathode active layerhaving redistributed sulfur-containing material of higher volumetricdensity than before the melting process.

Electrolytes, Separators, and Electrochemical Cells

The electrolytes used in electrochemical or battery cells function as amedium for the storage and transport of ions, and in the special case ofsolid electrolytes and gel electrolytes, these materials mayadditionally function as a separator between the anode and the cathode.Any liquid, solid, or gel material capable of storing and transportingions may be used, so long as the material is electrochemically andchemically unreactive with respect to the anode and the cathode, and thematerial facilitates the transport of lithium ions between the anode andthe cathode. The electrolyte must also be electronically non-conductiveto prevent short circuiting between the anode and the cathode.

Typically, the electrolyte comprises one or more ionic electrolyte saltsto provide ionic conductivity and one or more non-aqueous liquidelectrolyte solvents, gel polymer materials, or polymer materials.Suitable non-aqueous electrolytes for use in the present inventioninclude, but are not limited to, organic electrolytes comprising one ormore materials selected from the group consisting of liquidelectrolytes, gel polymer electrolytes, and solid polymer electrolytes.Examples of non-aqueous electrolytes for lithium batteries are describedby Dominey in Lithium Batteries, New Materials, Developments andPerspectives, Chapter 4, pp. 137-165, Elsevier, Amsterdam (1994).Examples of gel polymer electrolytes and solid polymer electrolytes aredescribed by Alamgir et al. in Lithium Batteries, New Materials,Developments and Perspectives, Chapter 3, pp. 93-136, Elsevier,Amsterdam (1994).

Examples of useful non-aqueous liquid electrolyte solvents include, butare not limited to, non-aqueous organic solvents, such as, for example,N-methyl acetamide, acetonitrile, acetals, ketals, sulfones, sulfolanes,aliphatic ethers, cyclic ethers, glymes, polyethers, phosphate esters,siloxanes, dioxolanes, N-alkylpyrrolidones, substituted forms of theforegoing, and blends thereof. Fluorinated derivatives of the foregoingare also useful.

Examples of ethers include, but are not limited to, dimethyl ether,diethyl ether, methylethyl ether, dipropyl ether, diisopropyl ether,dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane,diethoxyethane, 1,3-dimethoxypropane, tetrahydrofuran, tetrahydropyran,1,4-dioxane, and 1,3-dioxolane.

Examples of polyethers include, but are not limited to, diethyleneglycol dimethyl ether (diglyme), triethylene glycol dimethyl ether(triglyme), higher glymes, diethylene glycol divinylether, andtriethylene glycol divinylether.

Examples of sulfones include, but are not limited to, sulfolane,3-methyl sulfolane, 3-sulfolene, and non-symmetrical, non-cyclicsulfones, and fluorinated or partially fluorinated derivatives of theforegoing.

The specific choice of solvent will depend on several factors includingself discharge. The term “self discharge,” as used herein, relates tothe loss of capacity, or charge, when no external load is applied to thecell. An electrolyte comprising one or more non-aqueous electrolytesolvents and one or more electrolyte salts typically interacts with thelithium anode surface to form a solid electrolyte interface (SEI). TheSEI allows passage of lithium ions as the cell discharges and at thesame time it is desirable that the SEI protects the lithium surface fromfurther reactions with electrolyte, cathode discharge products, or othersoluble components of the cathode. In cells comprising electroactivesulfur-containing materials, the SEI should protect the lithium fromself discharge, for example, from reaction with possible cathodedischarge products such as sulfide ions, polysulfide ions, and othersulfur containing ions, and soluble cathode components such as sulfur.Preferred electrolyte solvents are those which provide low selfdischarge rates.

These liquid electrolyte solvents are themselves useful as plasticizersfor gel polymer electrolytes. Examples of useful gel polymerelectrolytes include, but are not limited to, those comprising one ormore polymers selected from the group consisting of polyethylene oxides,polypropylene oxides, polyacrylonitriles, polysiloxanes, polyimides,polyphosphazenes, polyethers, sulfonated polyimides, perfluorinatedmembranes (NAFION™ resins), polydivinyl polyethylene glycols,polyethylene glycol diacrylates, polyethylene glycol dimethacrylates,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing,and optionally plasticizers.

Examples of useful solid polymer electrolytes include, but are notlimited to, those comprising one or more polymers selected from thegroup consisting of polyethers, polyethylene oxides, polypropyleneoxides, polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing.

In addition to solvents, gelling agents, and polymers as known in theart for forming non-aqueous electrolytes, the non-aqueous electrolytemay further comprise one or more ionic electrolyte salts, also as knownin the art, to increase the ionic conductivity.

Examples of ionic electrolyte salts for use in the present inventioninclude, but are not limited to, LiSCN, LiBr, LiI, LiClO₄, LiAsF₆,LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄, LiPF₆, LiC(SO₂CF₃)₃, andLiN(SO₂CF₃)₂. Other electrolyte salts useful in the practice of thisinvention include lithium polysulfides (Li₂S_(x)), and lithium salts oforganic ionic polysulfides (LiS_(x)R)_(n), where x is an integer from 1to 20, n is an integer from 1 to 3, and R is an organic group, and thosedisclosed in U.S. Pat. No. 5,538,812 to Lee et al. The lithiumpolysulfides, Li₂S_(x), may be formed in situ in Li/S cells byself-discharge of the cells or during the discharge of the cells.Preferred ionic electrolyte salts are LiBr, LiI, LiSCN, LiBF₄, LiPF₆,LiAsF₆, LiSO₃CF₃, LiN(SO₂CF₃)₂, and LiC(SO₂CF₃)₃.

The electrochemical cells of the present invention may further comprisea separator interposed between the cathode and anode. Typically, theseparator is a solid non-conductive or insulative material whichseparates or insulates the anode and the cathode from each otherpreventing short circuiting, and which permits the transport of ionsbetween the anode and the cathode.

The pores of the separator may be partially or substantially filled withelectrolyte. Separators may be supplied as porous free standing filmswhich are interleaved with the anodes and the cathodes during thefabrication of cells. Alternatively, the porous separator layer may beapplied directly to the surface of one of the electrodes, for example,as described in PCT Publication No. WO 99/33125 to Carlson et al. and inU.S. Pat. No. 5,194,341 to Bagley el al.

A variety of separator materials are known in the art. Suitable solidporous separator materials include, but are not limited to, polyolefins,such as, for example, polyethylenes and polypropylenes, glass fiberfilter papers, and ceramic materials. Further examples of separators andseparator materials suitable for use in this invention are thosecomprising a microporous pseudo-boehmite layer, which may be providedeither as a free standing film or by a direct coating application on oneof the electrodes, as described in U.S. patent application Ser. Nos.08/995,089, now U.S. Pat. Nos. 6,153,337, and 09/215,112, now U.S. Pat.No. 6,306,545, by Carlson el al. of the common assignee. Solidelectrolytes and gel electrolytes may also function as a separator inaddition to their electrolyte function.

In one embodiment, the solid porous separator is a porous polyolefinseparator. In one embodiment, the solid porous separator comprises amicroporous pseudo-boehmite layer.

Cells and batteries of the present invention may be made in primary andsecondary types and in a variety of sizes and configurations which areknown to those skilled in the art. These battery design configurationsinclude, but are not limited to, planar, prismatic, jelly roll, w-fold,stacked, and the like. Although the methods of the present invention areparticularly suitable for use with thin film electrodes, they maynevertheless be beneficial in thick film designs.

It is generally accepted that, when low electric currents are desired,the electrodes within the cell should have as much mass and as littlesurface area as possible. At the expense of power density, this providesfor increased energy density while low electrode surface area minimizesundesirable self-discharge reactions. Conversely, when larger electricaldischarge currents are required, electrode surface area and powerdensity are maximized at the expense of energy density andself-discharge rate. Thin film electrodes provide high surface area andthereby high power density. Thin film electrodes may be incorporatedinto a number of battery design configurations, such as prismatic, jellyroll, w-fold and stacked configurations. Alternatively, designsincorporating both low and high surface area regions, as described inU.S. Pat. Nos. 5,935,724 and 5,935,728 to Spillman et al., may beincorporated into jelly roll and other configurations.

Thin film electrodes, in particular, may be configured into prismaticdesigns. With the drive to conserve weight, thin film barrier materialsare particularly preferred, e.g., foils. For example, PCT PublicationNo. WO 00/36678 (International Appl. NO. PCT/US99/30133) to Thibault etal. describes methods for preparing prismatic cells in which suitablebarrier materials for sealed casings, methods of filling cells withelectrolyte, and methods of sealing the casing, are described.

EXAMPLES

Several embodiments of the present invention are described in thefollowing examples, which are offered by way of illustration and not byway of limitation.

Example 1

Bis(methoxymethyl)polysulfide. A solution of sodium polysulfide wasprepared from Na_(s)S.9H₂O (12 g) and sulfur (1.6 g) in a solventmixture of water (20 mL) and ethanol (10 mL). To 16 mL of the sodiumpolysulfide solution was added chloromethyl methyl ether (3.9 g) slowlywith stirring at 25-27° C. Filtration of the solid (NaCl) and extractionwith ether led to the isolation of the bis(methoxymethyl)polysulfide(2.6 g) as a viscous oil. The bis(methoxymethyl)polysulfide wasdetermined by H¹ nmr to be a mixture of bis(methoxymethyl) mono-, di-,and trisulfides. Analysis of the oil gave the following results: C,31.0%; H, 5.20%; S, 45.08%. Calculated for C₄H₁₀O₂S₂: C, 31.16%; H,6.49%; S, 41.56%.

Example 2

Bis(methoxyethyl)disulfide. To 8 mL of the sodium polysulfide solutionof Example 1 was added 1-bromo-2-methoxy ethane (3.7 g) with stirring at22-25° C. Extraction of the reaction mixture with ether, washing of theethereal solution with water, and concentration gave an oil.Distillation of the oil yielded 1.0 g of bis(methoxyethyl)disulfide.Analysis of the oil gave the following results: C, 38.27%; H, 7.82%; S,36.18%. Calculated for C₆H₁₄O₂S₂: C, 39.56%; H, 7.69%; S, 35.16%.

Example 3

Bis(3-allyloxy-2-hydroxypropyl)trisulfide. A solution of sodiumpolysulfide was prepared from Na_(s)S.9H₂O (48 g) and sulfur (25.6 g) ina solvent mixture of water (40 mL) and ethanol (8 mL). This solution wasadded to allyl glycidyl ether (76 g) in ethanol (40 mL) containingNaHCO₃ (40 g) in portions during 1.5 hours at 27-35° C. Evaporation ofthe ethanol was followed by extraction with ether. After drying theethereal solution was concentrated to yieldbis(3-allyloxy-2-hydroxypropyl)trisulfide (89.3 g). Analysis of the oilgave the following results: C, 44.3%; H, 5.02%; S, 28.9%. Calculated forC₁₂H₂₂O₄S₃: C, 44.16%; H, 6.80%; S, 29.42%.

Example 4

Bis(vinyloxyethoxy-2-hydroxypropyl)polysulfide. A solution of sodiumpolysulfide was prepared from Na_(s)S.9H₂O (54.8 g) and sulfur (21.9 g)in water. The polysulfide solution was added with stirring to a mixtureof ethylene glycol vinyl glycidyl ether (82.3 g), triethylbenzylammonium chloride (5.7 g), and NaHCO₃ (82.3 g) during 3 hours at20° C. After 24 hours, water (200 mL) was added and the aqueous mixtureextracted with ether. Removal of the ether yieldedbis(vinyloxyethoxy-2-hydroxypropyl)polysulfide (86.4 g). Analysis of theoil gave the following results: C, 43.62%; H, 6.99%; S, 24.10%.Calculated for C₁₄H₂₆O₆S₃: C, 43.50%; H, 6.78%; S, 24.89%.

Example 5

Bis(2-hydroxy-2-phenylethyl)polysulfide. To a mixture of phenyloxirane(10 g), ethanol (5 mL), and NaHCO₃ (5 g) was added 8 mL of thepolysulfide solution of Example 3 during 1.5 hours at 20-25° C. Dilutionwith water and ether extraction yielded a yellow oil from which wasdistilled unreacted phenyloxirane (2.8 g). The residue (5 g) wasbis(2-hydroxy-2-phenylethyl)polysulfide.

Example 6

A cathode slurry, with a solid content of 14% by weight, was prepared ina solvent mixture of 80% isopropanol, 12% water, 5% 1-methoxy-2-propanoland 3% dimethyl ethanolamine (by weight). The solid slurry componentswere elemental sulfur (available from Aldrich Chemical Company,Milwaukee, Wis.), 65% by weight; Printex XE-2 (a trade name forconductive carbon available from Degussa Corporation, Akron, Ohio), 15%by weight; graphite (available from Fluka/Sigma-Aldrich, Milwaukee,Wis.), 15% by weight; TA22-8 resin (a trade name for an ethylacrylate-acrylic acid copolymer available from Dock Resins Corporation,Linden, N.J.), 4% by weight; and Ionac PFAZ-322 (a trade name fortrimethylol propane tris [β-(N-2-methyl aziridinyl) propionate],available from Sybron Chemicals Inc., Birmingham, N.J.), 1% by weight.The slurry was coated by a slot die coater onto both sides of a 18micron thick conductive carbon coated aluminum foil (Product No. 60303available from Rexam Graphics, South Hadley, Mass.), as a currentcollector. The coating was dried in the ovens of a slot die coater. Theresulting dry cathode active layer had a thickness of about 26 micronson each side of the current collector, with a loading of electroactivecathode material of about 1.1 mg/cm².

Cells were fabricated from the coated cathode. The anode was lithiumfoil of about 50 microns in thickness. The electrolyte was a 1.4 Msolution of lithium bis(trifluoromethylsulfonyl) imide, (lithium imide,available from 3M Corporation, St. Paul, Minn.) in a 42:58 volume ratiomixture of 1,3-dioxolane and dimethoxyethane. The porous separator usedwas 16 micron E25 SETELA (a trademark for a polyolefin separatoravailable from Mobil Chemical Company, Films Division, Pittsford, N.Y.).The above components were combined into a layered structure ofcathode/separator/anode, which was wound, soaked in the liquidelectrolyte, and inserted in vials, to form vial cells with an electrodearea of about 20 cm². The cells were charged and discharged at 0.25mA/cm² from 1.25 to 2.80 volts.

Example 7

Vial cells were prepared by the method of Example 6 except that 1 volume% (0.8 weight %) of the polysulfide of Example 1 was added to theelectrolyte prior to soaking. Charge and discharge of the cells wasperformed by the method of Example 6.

Example 8

Vial cells were prepared by the method of Example 6 except that 1 volume% (0.81 weight %) of the disulfide of Example 2 was added to theelectrolyte prior to soaking. Charge and discharge of the cells wasperformed by the method of Example 6.

Example 9

Vial cells were prepared by the method of Example 6 except that 1 volume% (0.98 weight %) of the trisulfide of Example 3 was added to theelectrolyte prior to soaking. Charge and discharge of the cells wasperformed by the method of Example 6.

Example 10

Vial cells were prepared by the method of Example 6 except that 5 volume% (4.9 weight %) of the trisulfide of Example 3 was added to theelectrolyte prior to soaking. Charge and discharge of the cells wasperformed by the method of Example 6.

Example 11

Vial cells were prepared by the method of Example 6 except that 3 volume% (3.2 weight %) of the polysulfide of Example 4 was added to theelectrolyte prior to soaking. Charge and discharge of the cells wasperformed by the method of Example 6.

Example 12

Vial cells were prepared by the method of Example 6 except that 10volume o/o (10.1 weight %) of the polysulfide of Example 4 was added tothe electrolyte prior to soaking. Charge and discharge of the cells wasperformed by the method of Example 6.

Example 13

Vial cells were prepared by the method of Example 6 except that 1 volume% (1.0 weight %) of the polysulfide of Example 5 was added to theelectrolyte prior to soaking. Charge and discharge of the cells wasperformed by the method of Example 6.

Example 14

Vial cells were prepared by the method of Example 6 except that 1 volume% (0.89 weight %) of chloromethyl methyl ether (CH₃OCH₂Cl) was added tothe electrolyte prior to soaking. Charge and discharge of the cells wasperformed by the method of Example 6.

The specific discharge capacity of the cells of Example 6, a comparativeexample, and the specific discharge capacities of the cells withcapacity-enhancing electrolyte additives of this invention, Examples7-14, are shown in Table 1.

TABLE 1 Specific Capacity vs. Electrolyte Additive Specific CumulativeSpecific Capacity (mAh/g) Capacity (mAh/g) Additive Cycle Cycle Cycle 30% Example Volume % 1 10 30 cycles Increase Example 6 0 1084 672 58120009 — Example 8 1 1080 561 — — — Example 9 1 1238 760 624 22109 11Example 10 5 1238 927 773 26888 34 Example 11 3 1238 827 665 23639 18Example 12 10 1298 819 — — — Example 13 1 1205 718 — — — Example 7 11233 678 543 20538  3 Example 14 1 1184 785 593 22212 11

Example 15

Cells were prepared by the procedure of Example 6, except that thelayered structure of cathode/separator/anode was wound and compressedwith the liquid electrolyte filling the separator and cathode to formprismatic cells with an electrode area of about 840 cm².Discharge-charge cycling of these cells was done at 0.42/0.24 mA/cm²,respectively, with discharge cutoff at a voltage of 1.5V and chargecutoff at 2.8V with 110% overcharge.

Example 16

An electrolyte was prepared by dissolving 2-(diethylamino)ethanethiolhydrochloride (0.86 g) in the lithium imide electrolyte of Example 6 (48g), placing lithium foil (0.15 g) in the solution, and allowing hydrogengas to be evolved during 4 days. After filtration, the resultingelectrolyte was a lithium imide solution containing 1.4% by weight ofthe lithium salt of 2-(diethylamino)ethane thiolate. Prismatic cellswere prepared by the procedure of Example 15 except that the lithium2-(diethylamino)ethanethiolate containing electrolyte solution abovereplaced the lithium imide electrolyte of Example 15. Discharge-chargecycling was performed by the method of Example 15.

Table 2 shows the discharge capacity vs. cycle number for prismaticcells of Example 15 (no capacity-enhancing additive) and Example 16 witha capacity-enhancing additive of this invention.

TABLE 2 Discharge Capacity vs. Cycle Number Additive Discharge CapacitymAh Example Weight % 20 Cycles 40 Cycles 60 Cycles Example 15 0 612 600543 Example 16 1.4 638 638 620

Example 17

Cyclic voltammetry, using as electrolyte 1.4 M lithiumbis(trifluoromethylsulfonyl) imide in a mixture of dimethoxyethane anddioxolane at a scan rate of 10 mV/sec with a nickel electrode, showedenhanced redox activity of 2-(diethylamino)ethanethiol in presence ofLi₂S₂ showing that the 2-(diethylamino)ethanethiol increased thesolubility of the Li₂S₂.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made without departingfrom the spirit and scope thereof.

What is claimed is:
 1. An electrochemical cell comprising: (a) a solid lithium anode; (b) a solid cathode comprising an electroactive sulfur-containing material; and (c) a non-aqueous electrolyte interposed between said anode and said cathode wherein said electrolyte comprises: (i) one or more lithium salts; (ii) one or more non-aqueous solvents; and (iii) one or more capacity-enhancing reactive components; wherein said capacity-enhancing reactive components comprise an electron transfer mediator of the formula:

 wherein: R⁴ is the same or different at each occurrence and is selected from the group consisting of H, alkyl, alkenyl, aryl, or substituted derivatives thereof; E is the same or different at each occurrence and is selected from the group consisting of O, NR⁵, and S; where R⁵ is alkyl, aryl, or substituted derivatives thereof; a is an integer from 0 to 1; and r is an integer from 2 to
 5. 2. The cell of claim 1, wherein said electron transfer mediator is present in the amount of 0.2% to 25% by weight of said electrolyte.
 3. The cell of claim 1, wherein said electron transfer mediator has an oxidation-reduction potential less than 2.2 V.
 4. The cell of claim 1, wherein said electron transfer mediator has an oxidation-reduction potential in the range of 1.5 V to about 2.0 V.
 5. The cell of claim 1, wherein said one or more capacity-enhancing reactive components increase the discharge capacity of the first charge-discharge cycle of said cell by greater than 10%.
 6. The cell of claim 1, wherein said one or more capacity-enhancing reactive components increase the total discharge capacities of 30 charge-discharge cycles of said cell by greater than 10%.
 7. The cell of claim 1, wherein said one or more capacity-enhancing reactive components increase the total discharge capacities of 30 charge-discharge cycles of said cell by greater than 30%.
 8. The cell of claim 1, wherein said one or more non-aqueous solvents are selected from the group consisting of ethers, cyclic ethers, polyethers, dioxolanes, sulfones, and sulfolanes.
 9. The cell of claim 1, wherein said one or more lithium salts are selected from the group consisting of LiBr, LiI, LiSCN, LiBF₄, LiPF₆, LiAsF₆, LiSO₃CF₃, LiN(SO₂CF₃)₂, LiC(SO₂CF₃)₃, (LiS_(x))_(z)R, and Li₂S_(x), where x is an integer from 1 to 20, z is an integer from 1 to 3, and R is an organic group.
 10. The cell of claim 1, wherein said electroactive sulfur-containing material comprises elemental sulfur.
 11. The cell of claim 1, wherein said electroactive sulfur-containing material, in its oxidized state, comprises one or more polysulfide moieties, —S_(m)—, where m is an integer equal to or greater than
 3. 12. The cell of claim 1, wherein said electroactive sulfur-containing material, in its oxidized state, comprises one or more polysulfide moieties, —S_(m) ⁻, where m is an integer equal to or greater than
 3. 13. The cell of claim 1, wherein said electroactive sulfur-containing material, in its oxidized state, comprises one or more polysulfide moieties, S_(m) ²⁻, where m is an integer equal to or greater than
 3. 14. The cell of claim 1, wherein said electroactive sulfur-containing material, in its oxidized state, is of the general formula C(S_(x))_(n) wherein x ranges from greater than 2.5 to about 50, and n is an integer equal to or greater than to
 2. 15. The cell of claim 1, wherein said electroactive sulfur-containing material comprises greater than 50% by weight of sulfur.
 16. The cell of claim 1, wherein said electroactive sulfur-containing material comprises greater than 75% by weight of sulfur.
 17. The cell of claim 1, wherein said electroactive sulfur-containing material comprises greater than 90% by weight of sulfur.
 18. The cell of claim 1, wherein said lithium anode is selected from the group consisting of lithium metal, lithium-aluminum alloys, lithium-tin alloys, lithium-intercalated carbons, and lithium-intercalated graphites.
 19. The cell of claim 1, wherein said cell has an energy density greater than 1000 Wh/Kg.
 20. The cell of claim 1, wherein said cell has an energy density greater than 1200 Wh/Kg.
 21. The cell of claim 1, wherein said cell has an energy density greater than 1500 Wh/Kg.
 22. The cell of claim 1, wherein said cell is a secondary electrochemical cell.
 23. The cell of claim 1, wherein said cell is a primary electrochemical cell.
 24. A method of making an electrochemical cell comprising the steps of: (a) providing a solid lithium anode; (b) providing a solid cathode comprising an electroactive sulfur-containing material; and (c) interposing a non-aqueous electrolyte between said anode and said cathode, wherein said electrolyte comprises: (i) one or more lithium salts; (ii) one or more non-aqueous solvents; and (iii) one or more capacity-enhancing reactive components; wherein said capacity-enhancing reactive components comprise an electron transfer mediator of the formula:

 wherein: R⁴ is the same or different at each occurrence and is selected from the group consisting of H, alkyl, alkenyl, aryl, or substituted derivatives thereof; E is the same or different at each occurrence and is selected from the group consisting of O, NR⁵, and S, where R⁵ is alkyl, aryl, or substituted derivatives thereof; a is an integer from 0 to 1; and r is an integer from 2 to
 5. 